PROJECT SUMMARY Personalizing medication dose and dosing intervals for the individual patient with inflammatory bowel disease (IBD) would revolutionize treatment. Crohn?s disease is a relapsing and remitting disease of the large and small intestines that results in progressive inflammation and eventual damage to the bowel. Infliximab, and similar medications that target tumor necrosis factor-alpha (TNF?) in Crohn?s disease patients, can reverse epithelial damage, promote bowel healing and prevent unwanted Crohn?s sequela such as fistula or abscess formation. In children and young adolescents with Crohn?s disease, there has been a paradigm shift in anti-TNF use in order to improve rates of sustained remission and reverse growth failure. While therapeutic drug monitoring has improved the overall durability of infliximab, lifetime rates of surgery for intestinal strictures have remained stagnant with conventional, weight-based dosing. More recent pharmacokinetic studies in adults and children with Crohn?s disease have found infliximab clearance is affected by antigen load (inflammatory burden with TNF?), patient weight, serum albumin, fecal loss of drug and immunogenicity (antibodies to drug). With this substantial variability with infliximab clearance, many clinicians utilize dynamic dosing strategies to account for individual pharmacokinetics such as more frequent dosing intervals for hypoalbuminemia or increasing the dose from 5 to 10 mg/kg for severe colitis. We hypothesize that incorporating patient-specific characteristics and novel blood biomarkers as covariates will result in more accurate prediction of infliximab clearance supporting the use of a Bayesian adaptive-dosing approach in clinical practice. To test this hypothesis, we have proposed a pharmacokinetic evaluation of a rigorously monitored pediatric Crohn disease cohort who have provided longitudinal biospecimens during the first year of infliximab therapy. In Aim 1, we will develop a pharmacokinetic model based on significant covariates that influence infliximab clearance during induction. In Aim 2, we will construct a pharmacokinetic model based on significant covariates that influence infliximab clearance during maintenance. In conclusion, there is a critical knowledge gap between the integration of pharmacodynamic biomarkers with infliximab dosing strategies and even greater provider variability between timing of therapeutic drug monitoring and the subsequent dosing decisions. Our overarching goal is to minimize these current gaps with improved, more dynamic assessments of disease burden and infliximab clearance to develop an innovative dosing strategy and improve patient outcomes with anti-TNF therapies.